1. Field of the Invention
The present invention relates to a brazing construction and a brazing method for an abradable sealing material such as those that may be applied to an internal surface of a casing of a turbine, opposing rotor blades of the turbine.
2. Description of the Related Art
This type of abradable sealing material is generally called honeycomb seal because it appears to have a honeycomb construction when seen from the turbine rotor blade side.
Honeycomb seal is a thin tabular sealing material which is attached to an inner periphery face of a split ring on the casing positioned opposite the rear rotor blade of a gas turbine, and which seals the gap between the turbine rotor blade and the split ring. Also, this honeycomb seal is formed to have excellent abradability (ease of abrasion), so that its own surface will be abraded when the tip of a turbine rotor blade makes contact for some reason (heat expansion etc.), and so it prevents damage to the turbine rotor blade and the split ring caused by contact (see Japanese Unexamined Patent Application, First Publication 11-6446 and Japanese Unexamined Patent Application, First Publication 11-13404).
FIG. 6 shows an enlargement of a schematic configuration of a honeycomb seal, and FIG. 7 shows a sectional view on VI—VI of FIG. 6. In FIG. 6, reference numeral 1 denotes a honeycomb seal fixed by brazing to the upper surface of a base material 10 which is a member at the casing side (split ring or similar). The honeycomb seal 1 is formed as a tabular member that has a cellular compartment construction in honeycomb form comprised of empty compartments and partitions in order to have abradability in the direction A perpendicular to the face of the base material 10 and sealing ability in a specified direction B parallel to the face of the base material 10. Reference numeral 3 denotes numerous cells (cellular compartments) in honeycomb form.
Because this honeycomb seal 1 forms honeycomb-shaped cells 3 by means of the combination of a plurality of thin corrugated sheets 2 standing vertically in the direction A perpendicular to the face of the base material 10, it has micro gaps 5 in the overlapped parts 4 of each thin corrugated sheet 2. Here, the direction B in which the sealing property is created is orthogonal to the direction in which the thin corrugated sheets 2 extend.
When a honeycomb seal 1 of this kind of construction is brazed to the base material 10, the operation proceeds according to the processes shown in FIG. 8. Firstly, as shown in step a in FIG. 8, the honeycomb seal 1 constructed by combining each of the thin corrugated sheets 2, is placed on the base material 10 and temporarily fixed by spot welding.
Next, as shown in step b in FIG. 8, a powdered brazing filler metal 7 is sprinkled over the honeycomb seal 1 into each of the cells 3 (cellular compartments) and the powder of the brazing filler metal 7 spreads evenly on the base material 10. Alternatively, as shown in steps c and d in FIG. 8, a sheet form of brazing filler metal 7 formed using a binding agent is placed on top of the honeycomb seal 1 and dissolved with an acetone 8 so that it falls into each of the cells 3.
Subsequently, as shown in step e in FIG. 8, the assembly is placed in a heating furnace 9 and the honeycomb seal 1 is brazed to the base material 10.
Incidentally, although the requirement of the product is that the honeycomb seal 1 impart excellent abradability to the surface side opposing the turbine rotor blade, there is a concern that a defect may arise when brazing is carried out as described above.
Specifically, because the honeycomb seal 1 is constructed by the combination of a plurality of thin corrugated sheets 2 as mentioned above, it has micro gaps 5 in the overlapped parts 4 of each of the thin corrugated sheets 2. These micro gaps 5 extend in the direction A perpendicular to the face of the base material 10, and when the honeycomb seal 1 is brazed to the base material 10, then as shown in FIG. 7, the brazing filler metal 7 infiltrates into the micro gaps 5 by capillary action and the rigidity of the honeycomb seal 1 increases, and as a result there is a concern that the abradability of the same area may decrease. If the abradability decreases in this way, it will no longer be able to function as a honeycomb seal as the wear on the turbine rotor blade side becomes severe.